First of all, bitcoin is a decentralised currency — there is no
central bank, no mint printing money, no governing authority
maintaining records.

But records have to be maintained somehow, to ensure
there is no double-spending of the currency. Instead members of
the network collectively contribute processing power from their
computers to maintain bitcoin's integrity. And every time a
transaction is made, a record of it is sent out to be recorded
immutably in a public ledger. This ledger is the blockchain.

It allows bitcoin users to cut out the middleman — one user can
send another a sum of money, anywhere in the world, without
having to rely on a financial institution. The transactions are
effectively set in stone, with records distributed permanently
across the entire network.

Nasdaq is hoping to bring the efficiency promised by the
blockchain to other areas of finance, potentially dramatically
reducing the need for lawyers and intermediaries. For now, Nasdaq
is implementing the technology in its Nasdaq Private Market,
which The Journal reports is "a fledgling marketplace
launched in January 2014 to handle pre-IPO trading among private
companies."

Previously maintained by "largely informal systems, including
spreadsheets maintained by lawyers who verify transactions by
hand," the blockchain could automate the entire process. Once a
deal is done, the parties would cryptographically sign a
contract, and the rights would be transferred over almost
instantaneously — no lawyers required.